Elastomers are especially desirable for use within various aircraft and other applications in view of their unique ability to resiliently flex, stretch, compress, and/or seal without substantial deterioration during accommodation of the particular loads impressed thereon. The inherent softness property of the elastomers, however, sometimes manifests itself as a considerable problem which must of course be resolved in order to maintain the integrity and operation of the particular system of which the elastomer is an integral part. The foregoing is especially true, for example, in those applications wherein the elastomer is to be fastened to basic structural components, and wherein further, the elastomer-fastener system is subjected to considerably large stretching and/or flexing displacements or load forces. Specifically, the load forces and/or moments impressed upon the elastomer of the joint system cannot adequately be transferred from the elastomer to the fastener without some type of separation failure being experienced within the vicinity of the fastener locus.
The foregoing can be better appreciated if reference is made to FIGS. 1 and 2 which illustrate two conventional methods or systems of attaching load-transmitting elastomers to aircraft structural components in order to provide an attachment joint. With specific reference being made to FIG. 1, there is shown an attachment joint generally indicated by the reference character 100. The joint includes, for example, an aircraft structural component 102 which may be a part of the aircraft wing leading edge assembly, and the elastomer 104 which is adapted to be interposed between the wing leading edge component 102 and, for example, the main front spar, not shown, of the wing so as to thereby transmit load forces or flexing moments therebetween.
The elastomer 104 may comprise any suitable elastomer fabricated, for example, from silicone rubber, and it is seen that the elastomer 104 is secured to the aircraft structural component 102 by suitable fastening means which may comprise bolts 106 and nuts 108, only one set of the fastening means being shown. In order to enhance the structural integrity of the attachment joint, it is appreciated that the aircraft structural component, as viewed in cross-section, has a stepped configuration such that, for example, the elastomer 104 may be seated and supported upon the lowermost stepped portion 110 of the component 102. In a similar manner, the elastomer, within the vicinity of the joint or connection locus, is also provided with a stepped configuration as views in cross-section and as indicated by the reference character 112. In this manner, a cover plate 114 may be provided so as to seat upon the uppermost stepped portion 116 of component 102 as well as upon the stepped portion 112 of elastomer 104. When this structural system is then fastened together, it is seen that the upper surface 118 of component 102, the upper surface 120 of cover plate 114, and the upper surface 122 of elastomer 104 are all flush or in alignment with respect to each other within a horizontal plane. To complete the entire fastening assembly or attachment joint, clamp-up bushings 124, only one of which is shown, are bonded within the rubber elastomer 104 at the fastener loci so as to annularly surround the fastener bolts 106 and be interposed between the lowermost stepped portion 110 of the structural component 102 and the cover plate 114. In this manner, when the bolt fastening means are tightened, that portion of the elastomer 104 interposed between the cover plate 114 and the stepped portion 110 of component 102 is not excessively stressed by the resulting compression forces.
While the attachment joint system illustrated in FIG. 1 would thus appear to exhibit the requisite structural integrity required under the various operating load conditions to which such a system would normally be subjected, in fact the attachment joint illustrated will exhibit failure within the vicinity of the fastener as opposed to, for example, failure of the elastomer itself when substantially large stretching and/or flexing displacements, loads, and moments are impressed thereon. This is due to the fact that the elastomer 104 will experience separation from the bushings 124 due to inherent incompatibility therebetween, especially under such severe load, displacement, or moment conditions.
Considering now the attachment joint system illustrated within FIG. 2, it is initially noted that this system is similar to that illustrated within FIG. 1, and therefore, the reference characters applied to the various components of the system are similar although are also noted to be within the 200 range whereas those of FIG. 1 were within the 100 range. The system of FIG. 2 was constructed so as to serve as an improved alternative to the system illustrated within FIG. 1 and has been generally designated by the reference character 200. In this attachment system, it is noted that the bushings 124 have been eliminated, and the elastomer 204 has been reinforced with one or more plies or layers of a suitable fabric or FIBERGLAS (Registered Trademark) 226, although only one ply of the fabric is illustrated. The fabric or FIBERGLAS 226 is embedded within the elastomer 204 and extends throughout the same within the vicinity of the fastener loci in order to allegedly improve the structural integrity of the illustrated attachment joint. Nevertheless, as with the attachment joint of the embodiment illustrated within FIG. 1, the attachment joint embodied within FIG. 2 has also experienced failure at the fastener attachment loci in lieu of failure of the elastomer per se.
In particular, in the instance wherein one or more plies of fabric reinforcement are employed within the elastomer 204, the reinforced elastomer still exhibits failure under the impressed load, displacement, and moment conditions due to insufficient reinforcement at the fastener sites. In other words, even when reinforced with multiple fabric plies, the composite reinforced elastomer is still inherently incompatible with the fastening means and does not have the requisite structural strength or rigidity within the vicinity of the fastener sites to in fact distribute the impressed load forces, displacements, and moments to the fastening means without separating from the fasteners and thus exhibiting failure.
In a similar manner, when the elastomer is reinforced with one or more plies or layers of FIBERGLAS, the latter separate from the elastomer in shear due, for example, to the different tensile stretch properties characteristic of the elastomer and FIBERGLAS components. In addition, the rubber elastomer has been observed to have subsequently separated or torn away from the fastening means thereby again resulting in failure of the joint.
A need therefore exists for an improved reinforced elastomer attachment joint which will in fact be able to withstand and transmit substantially large stretching and flexing displacements, loads, and moments with respect to basic support structure without exhibiting failure or a deterioration in structural integrity under such operating conditions.
Accordingly, it is an object of the present invention to provide a new and improved reinforced elastomer attachment joint.
Another object of the present invention is to provide a new and improved reinforced elastomer attachment joint which will overcome the operational disadvantages characteristic of prior art elastomer attachment joints.
Still another object of the present invention is to provide a new and improved reinforced elastomer attachment joint which is capable of withstanding substantially large stretching and flexing displacements, load forces, and moments impressed thereon during operational modes without experiencing or exhibiting failure.
Yet another object of the present invention is to provide a new and improved reinforced elastomer attachment joint which is capable of withstanding substantially large stretching and flexing displacements, load forces, and moments impressed thereon during operational modes without experiencing or exhibiting deterioration of structural integrity.
Still yet another object of the present invention is to provide a new and improved reinforced elastomer attachment joint which is capable of transmitting substantially large stretching and flexing displacements, load forces, and moments to basic support structure without experiencing or exhibiting failure.
Yet still another object of the present invention is to provide a new and improved reinforced elastomer attachment joint which is capable of transmitting substantially large stretching and flexing displacements, load forces, and moments to basic support structure without experiencing or exhibiting deterioration of structural integrity.
A further object of the present invention is to provide a new and improved reinforced elastomer attachment joint wherein areas of non-compatibility between the various components of the joint or system have been eliminated so as to in fact achieve the maintenance of the structural integrity of the system and thereby prevent structural failure or deterioration of the system.
A yet further object of the present invention is to provide a new and improved reinforced elastomer attachment joint wherein the system or joint exhibits sufficient reinforcement, structural integrity, and rigidity, particularly within the vicinity of the basic support structure and the fastening means thereof such that the system or joint will not experience or exhibit failure or deterioration under operational conditions.
A still further object of the present invention is to provide a new and improved reinforced elastomer attachment joint which is relatively simple in structure and economical to manufacture.
A still yet further object of the present invention is to provide a new and improved reinforced elastomer attachment joint which facilitates the elimination of several of the hardward components characteristics of prior art or conventional elastomer attachment joints or systems.